Fundus observation apparatus

ABSTRACT

The controller  210  changes the projection region of the Landolt ring T on the fundus Ef by changing, based on the scanning region R, the relative display position of the Landolt ring T and the fixation target V on the LCD  39 , thereby overlapping the scanning region R and the projection region each other. Under this condition, the fundus observation apparatus  1  executes the eyesight measurement and OCT measurement, obtains the eyesight value at the site of interest of the fundus Ef, and forms a tomographic image of the fundus Ef in the scanning region R. The controller  210  stores in the storage  212  the eyesight value at the site of interest and the tomographic image corresponding to the scanning line closest to the measurement position of eyesight while correlating them with each other, and allows them to be displayed on the display device  3.

RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.13/266,148 filed on Oct. 25, 2011, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present invention relates to a fundus observation apparatusconfigured to form images of a fundus of an eye by using opticalcoherence tomography.

BACKGROUND ART

In recent years, optical coherence tomography that forms images of thesurface morphology and internal morphology of an object by using a lightbeam from a laser light source or the like has attracted attention.Unlike an X-ray CT apparatus, optical coherence tomography isnoninvasive to human bodies, and is therefore expected to be utilized inthe medical field and biological field.

Patent Document 1 discloses a device to which optical coherencetomography is applied. This device has such a configuration that: ameasuring arm scans an object by a rotary deflection mirror (a Galvanomirror); a reference arm is provided with a reference mirror; and aninterferometer is mounted at the outlet to analyze, by a spectrometer,the intensity of an interference light of light fluxes from themeasurement arm and the reference arm. Moreover, the reference arm isconfigured to gradually change the light flux phase of the referencelight by discontinuous values.

The device of Patent Document 1 uses a technique of so-called “FourierDomain OCT (Optical Coherence Tomography).” That is to say, the deviceirradiates a low coherence light beam to an object, superposes thereflected light and the reference light to generate an interferencelight, and acquires the spectral intensity distribution of theinterference light to execute Fourier transform, thereby imaging themorphology in the depth direction (the z-direction) of the object. Thetechnique of this type is also called Spectral Domain.

Furthermore, the device described in Patent Document 1 is provided witha Galvano mirror that scans with a light beam (a signal light), and isthereby configured to form an image of a desired measurement targetregion of the object. Because this device is configured to scan with thelight beam only in one direction (the x-direction) orthogonal to thez-direction, an image formed by this device is a two-dimensionaltomographic image in the depth direction (the z-direction) along thescanning direction (the x-direction) of the light beam.

Patent Document 2 discloses a technique of scanning with a signal lightin the horizontal direction (x-direction) and the vertical direction(y-direction) to form a plurality of two-dimensional tomographic imagesin the horizontal direction, and acquiring and imaging three-dimensionaltomographic information of a measured range based on the tomographicimages. As the three-dimensional imaging, for example, a method ofarranging and displaying a plurality of tomographic images in thevertical direction (referred to as stack data or the like), and a methodof executing a rendering process on a plurality of tomographic images toform a three-dimensional image are considered.

Patent Documents 3 and 4 disclose other types of OCT devices. PatentDocument 3 describes an OCT device that images the morphology of anobject by sweeping the wavelength of light that is irradiated to anobject, acquiring the spectral intensity distribution based on aninterference light obtained by superposing the reflected lights of thelight of the respective wavelengths on the reference light, andexecuting Fourier transform. Such an OCT device is called a Swept Sourcetype or the like. The Swept Source type is a kind of the Fourier Domaintype.

Further, Patent Document 4 describes an OCT device that irradiates alight having a predetermined beam diameter to an object and analyzes thecomponents of an interference light obtained by superposing thereflected light and the reference light, thereby forming an image of theobject in a cross-section orthogonal to the travelling direction of thelight. Such an OCT device is called a full-field type, en-face type orthe like.

Patent Document 5 discloses a configuration in which the OCT is appliedto the ophthalmologic field. Before the OCT device was applied to theophthalmologic field, a fundus observation apparatus such as a retinalcamera had been used (for example, refer to Patent Document 6).

Compared to a retinal camera that can only photograph a fundus from thefront, a fundus observation apparatus using OCT has a merit thattomographic images and 3-dimensional images of a fundus are obtained.Therefore, contribution to increase of the diagnosis accuracy and earlydetection of a lesion are expected.

The fundus observation apparatus using optical coherence tomography thusoccupies an important place in diagnosis and treatment of diseases.However, in reality, eyesight values are currently used in order todetermine the necessity of treatment and the presence or absence of itseffect.

This is due to the fact that the main purpose of treatment is theimprovement of eyesight, and the change in the morphology of the fundus(for example, hole shrinkage due to treatment of the macular hole) canbe confirmed by the fundus observation apparatus, but it cannot bedetermined whether or not the change in the morphology results inimprovement of eyesight without relying on eyesight measurement.

It should be noted that eyesight measurement is an eye examination inwhich a visual target for measuring eyesight such as a Landolt ring ispresented to the subject, commonly carried out using a subjectiveoptometer (see, for example, Patent Document 7).

PRIOR ART DOCUMENTS Patent Documents [Patent Document 1]

-   Japanese Unexamined Patent Application Publication No. Hei 11-325849

[Patent Document 2]

-   Japanese Unexamined Patent Application Publication No. 2002-139421

[Patent Document 3]

-   Japanese Unexamined Patent Application Publication No. 2007-24677

[Patent Document 4]

-   Japanese Unexamined Patent Application Publication No. 2006-153838

[Patent Document 5]

-   Japanese Unexamined Patent Application Publication No. 2008-73099

[Patent Document 6]

-   Japanese Unexamined Patent Application Publication No. Hei 9-276232

[Patent Document 7]

-   Japanese Unexamined Patent Application Publication No. 2008-148930

DISCLOSURE OF THE INVENTION Problem that the Invention is to Solve

However, with eyesight measurement, it cannot be determined which siteof the fundus is used to see the target (i.e., it cannot be determinedwhich site of the fundus is projected with the target), and it cannot bedetermined if the eyesight value of the treatment sight has actuallyimproved. For example, in a healthy eye, the target is projected on themacula flava due to the target being recognized in the macula flavahaving the highest visual ability; however, when there is a disorder inthe macula flava, the target tends to be captured by a site other thanthe macula flava, so the eyesight value of the affected site actuallycannot always be measured. In such a case, it is preferable that thevisual ability be able to be confirmed by conducting eyesightmeasurement at the site of interest (treatment site, diagnosed site,etc.) of the fundus, while being able to confirm the morphology of thefundus by obtaining an image of the site of interest. However,conventional devices have not been able to obtain an image of theeyesight measurement position. Consequently, for example, it has notbeen possible to determine whether or not the treatment is actuallyreflected in improvement of eyesight.

Moreover, the viewing angle (size) of the visual target for measuringeyesight projected on the fundus is sometimes changed due to therefractive power (eye refractive power) of the eye, and there has been aproblem in that the eyesight value cannot be precisely measured in sucha case.

Furthermore, it is also conceivable that a conventional fundusobservation apparatus is added with a target presenting function, but insuch a case the subject has to simultaneously visually confirm thesignal light, the fixation target and the visual target for measuringeyesight, increasing the complexity of the examination and possiblycausing adverse effects.

This invention resolves the above-mentioned problem, with the purpose ofproviding a fundus observation apparatus capable of obtaining an imageat the eyesight measurement site of the fundus.

Means for Solving the Problem

In order to achieve the aforementioned objects, an invention accordingto claim 1 is a fundus observation apparatus comprising: a projectionpart that includes a display part to display a visual target formeasuring eyesight, and projects, via a predetermined optical path, saiddisplayed visual target for measuring eyesight to the fundus of an eye;a light source that outputs low-coherence light; an optical system thatsplits said output low-coherence light into signal light and referencelight, generates interference light by superposing said signal lightthat has passed through said fundus via said predetermined optical pathand said reference light that has passed through a reference opticalpath, and detects said interference light; a scanning part that scanssaid fundus with said signal light; a controlling part that overlaps theprojection region of said visual target for measuring eyesight projectedby said projection part and the scanning region of said signal lightscanned by said scanning part each other; an image forming part thatforms an image of said fundus based on the detection results ofinterference light generated by superposing said signal light with whichsaid scanning region is scanned and said reference light; and a storagepart that stores said formed image and an eyesight value measured usingsaid visual target for measuring eyesight while correlating them witheach other.

Further, an invention according to claim 2 is the fundus observationapparatus according to claim 1, wherein said controlling part controlssaid projection part based on the scanning region of said signal lightscanned by said scanning part to overlap the projection region of saidvisual target for measuring eyesight in said fundus on the scanningregion of said signal light.

Further, an invention according to claim 3 is the fundus observationapparatus according to claim 2, wherein: said display part displays afixation target for fixing said eye along with said visual target formeasuring eyesight; said projection part projects said displayedfixation target on said fundus along with said visual target formeasuring eyesight; and said controlling part changes said projectionregion by changing, based on said scanning region, the relative displaypositions of said visual target for measuring eyesight and said fixationtarget displayed by said display part.

Further, an invention according to claim 4 is the fundus observationapparatus according to claim 1, wherein said controlling part controlssaid scanning part based on the display position of said visual targetfor measuring eyesight displayed by said display part to overlap thescanning region of said signal light in said fundus on the projectionregion of said visual target for measuring eyesight.

Further, an invention according to claim 5 is the fundus observationapparatus according to claim 1, wherein said controlling part allowssaid visual target for measuring eyesight corresponding to differenteyesight values to be projected on said fundus, by allowing said visualtarget for measuring eyesight of different sizes to be displayed on saiddisplay part to change the size of said projection region.

Further, an invention according to claim 6 is the fundus observationapparatus according to claim 5, wherein: said predetermined optical pathis provided with a focusing lens that moves along an optical axisthereof to change the focus position of light towards said fundus; andsaid controlling part adjusts the size of said visual target formeasuring eyesight displayed on said display part based on the positionof said focusing lens.

Further, an invention according to claim 7 is the fundus observationapparatus according to claim 5, further comprising an operation part forinputting response contents for said visual target for measuringeyesight projected on said fundus, wherein said controlling part changesthe size of said visual target for measuring eyesight displayed on saiddisplay part based on said input response contents, and determines theeyesight value of said eye based on said response contents according tothis change.

Further, an invention according to claim 8 is the fundus observationapparatus according to claim 1, further comprising an operation part forinputting response contents for said visual target for measuringeyesight projected on said fundus, wherein said controlling partcontrols said projection part to project said visual target formeasuring eyesight corresponding to a predetermined eyesight value tosaid fundus, determines whether said input response contents for thisvisual target for measuring eyesight are true or false, and if it isdetermined that they are correct, then controls said scanning part toscan said scanning region overlapping the projection region with saidsignal light.

Further, an invention according to claim 9 is the fundus observationapparatus according to claim 1, wherein said light source outputsinvisible light as said low-coherence light.

Further, an invention according to claim 10 is the fundus observationapparatus according to claim 9, wherein said light source outputsnear-infrared light of center wavelength within the range substantiallyfrom 1050 to 1060 nm.

Effect of the Invention

According to the fundus observation apparatus related to the presentinvention, an image of the scanning region of the signal light on thefundus can be formed with said scanning region being superposed on theprojection region of the visual target for measuring eyesight, and it ispossible to measure the eyesight in the projection region and then storethe formed image and the measured eyesight value while associating themwith each other, allowing an image of the eyesight measurement site ofthe fundus to be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an example of a configuration of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 2 is a schematic view showing an example of a configuration of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 3 is a schematic block diagram showing an example of aconfiguration of an embodiment of a fundus observation apparatusaccording to the present invention.

FIG. 4 is a flowchart showing an example of an action of an embodimentof a fundus observation apparatus according to the present invention.

FIG. 5 is a schematic view for explaining an example of an action of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 6 is a schematic view for explaining an example of an action of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 7 is a flowchart showing an example of an action of an embodimentof a fundus observation apparatus according to the present invention.

FIG. 8 is a schematic view for explaining an example of an action of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 9 is a schematic view for explaining an example of an action of anembodiment of a fundus observation apparatus according to the presentinvention.

FIG. 10 is a schematic block diagram showing an example of aconfiguration of a modification example of an embodiment of a fundusobservation apparatus according to the present invention.

MODE FOR CARRYING OUT THE INVENTION

An example of an embodiment of a fundus observation apparatus accordingto the present invention will be described in detail with reference tothe drawings.

The fundus observation apparatus according to the present inventionforms tomographic images of a fundus using optical coherence tomography.Optical coherence tomography of an arbitrary type involving scanningwith a signal light such as a Fourier Domain type, a swept source type,etc. are applicable to the fundus observation apparatus. It should benoted that an image obtained by optical coherence tomography issometimes referred to as an OCT image. Furthermore, a measuring actionfor forming an OCT image is sometimes referred to as an OCT measurement.

In the following embodiments, a configuration to which aFourier-Domain-type is applied will be described in detail. To bespecific, in these embodiments, similar to a device disclosed in PatentDocument 5, a fundus observation apparatus that is capable of obtainingboth tomographic images and photographed image of a fundus will bepicked up.

[Configuration]

A fundus observation apparatus 1, as shown in FIG. 1 and FIG. 2,includes a retinal camera unit 2, an OCT unit 100, and an arithmetic andcontrol unit 200. The retinal camera unit 2 has almost the same opticalsystem as a conventional retinal camera. The OCT unit 100 is providedwith an optical system for obtaining an OCT image of a fundus. Thearithmetic and control unit 200 is provided with a computer thatexecutes various arithmetic processes, control processes, and so on.

[Retinal Camera Unit]

The retinal camera unit shown in FIG. 1 is provided with an opticalsystem for forming a 2-dimensional image (fundus image) representing thesurface morphology of the fundus Ef of an eye E. Fundus images includeobservation images, photographed images, etc. The observation image is,for example, a monochrome image formed at a prescribed frame rate usingnear-infrared light. The photographed image is, for example, a colorimage captured by flashing visible light. It should be noted that theretinal camera unit 2 may also be configured so as to be capable ofcapturing other types of images such as a fluorescein angiography imageor an indocyanine green fluorescent image.

The retinal camera unit 2 is provided with a chin rest and a foreheadplacement for retaining the face of the subject, similar to aconventional retinal camera. Moreover, like a conventional retinalcamera, the retinal camera unit 2 is provided with an illuminationoptical system 10 and an imaging optical system 30. The illuminationoptical system 10 irradiates an illumination light to the fundus Ef. Theimaging optical system 30 guides a fundus reflected light of theillumination light to imaging devices (CCD image sensors 35, 38).Moreover, the imaging optical system 30 guides a signal light LS comingfrom the OCT unit 100 to the fundus Ef, and guides the signal lightpropagated through the fundus Ef to the OCT unit 100.

An observation light source 11 of the illumination optical system 10comprises, for example, a halogen lamp. Light (observation illuminationlight) output from the observation light source 11 is reflected by areflection mirror 12 with a curved reflection surface, and becomes nearinfrared after passing through a visible cut filter 14 via a condenserlens 13. Furthermore, the observation illumination light is onceconverged near an imaging light source 15, reflected by a mirror 16, andpasses through relay lenses 17, 18, diaphragm 19, and relay lens 20.Then, the observation illumination light is reflected on the peripheralpart (the surrounding region of an aperture part) of an aperture mirror21 and illuminates the fundus Ef via an object lens 22.

The fundus reflection light of the observation illumination light isrefracted by the object lens 22, passes through the aperture part formedin the center region of the aperture mirror 21, passes through adichroic mirror 55 and, travels through a focusing lens 31, and isreflected by a dichroic mirror 32. Furthermore, the fundus reflectionlight passes through a half-mirror 40 and forms an image on the lightreceiving surface of the CCD image sensor 35 by a condenser lens 34after being reflected by a dichroic mirror 33. The CCD image sensor 35detects, for example, the fundus reflection light at a prescribed framerate. An image (observation image) K based on the fundus reflectionlight detected by the CCD image sensor 35 is displayed on a displaydevice 3.

The imaging light source 15 consists of, for example, a xenon lamp. Thelight (imaging illumination light) output from the imaging light source15 is irradiated to the fundus Ef via a route that is similar to theobservation illumination light. The fundus reflection light of theimaging illumination light is guided to the dichroic mirror 33 via thesame route as that of the observation illumination light, passes throughthe dichroic mirror 33, and forms an image on the light receivingsurface of the CCD image sensor 38 by a condenser lens 37 after beingreflected by a mirror 36. An image (photographed image) H based on thefundus reflection light detected by the CCD image sensor 38 is displayedon the display device 3. It should be noted that the display device 3for displaying an observation image K and the display device 3 fordisplaying a photographed image H may be the same or different.

An LCD (Liquid Crystal Display) 39 displays a fixation target or avisual target for measuring eyesight. The fixation target is a visualtarget for fixing the eye E, and is used when photographing a fundus orforming a tomographic image. The visual target for measuring eyesight isa visual target used for measuring an eyesight value of the eye E, forexample, such as Landolt rings. It should be noted that the visualtarget for measuring eyesight is sometimes simply referred to as atarget.

Part of the light output from the LCD 39 is reflected by a half-mirror40, reflected by the dichroic mirror 32, passes through the aperturepart of the aperture mirror 21 via the focusing lens 31 as well as adichroic mirror 55, is refracted by the object lens 22 and projected tothe fundus Ef. LCD 39 is an example of a “display part” of theinvention. Moreover, LCD 39 and the above-mentioned group of opticalelements that project light output from LCD 39 on the fundus Ef are a“projection part” of the invention.

By changing a display position of the fixation target on the screen ofthe LCD 140, it is possible to change a fixation position of the eye E.As the fixation position of the eye E, there are a position foracquiring an image centered on the macula of the fundus Ef, a positionfor acquiring an image centered on the optic papilla, a position foracquiring an image centered on the fundus center between the macula andthe optic papilla, and so on, for example, as in conventional retinalcameras.

Furthermore, as with conventional fundus cameras, the retinal cameraunit 2 is provided with an alignment optical system 50 and a focusoptical system 60. The alignment optical system 50 generates a target(alignment target) for matching the position (alignment) of the deviceoptical system with respect to the eye E. The focus optical system 60generates a target (split target) for matching the focus with respect tothe eye Ef.

Light (alignment light) output from the LED (Light Emitting Diode) 51 ofthe alignment optical system 50 is reflected by the dichroic mirror 55via diaphragms 52, 53 and a relay lens 54, passes through the aperturepart of the aperture mirror 21, and is projected onto the cornea of theeye E by the object lens 22.

Part of cornea reflection light of the alignment light is transmittedthrough the dichroic mirror 55 via the object lens 22 and the aperturepart, passes through the focusing lens 31, is reflected by the dichroicmirror 32, transmitted through the half-mirror 40, reflected by thedichroic mirror 33, and projected onto the light receiving surface ofthe CCD image sensor 35 by the condenser lens 34. An image (alignmenttarget) captured by the CCD image sensor 35 is displayed on the displaydevice 3 along with the observation image K. A user conducts alignmentby an operation that is the same as conventional fundus cameras. Itshould be noted that alignment may be performed, by an arithmetic andcontrol unit 200, as a result of analyzing the position of the alignmenttarget and moving the optical system.

In order to conduct focus adjustment, the reflection surface of areflection rod 67 is provided in a slanted position on the light path ofthe illumination optical system 10. Light (focus light) output from anLED 61 of the focus optical system 60 passes through a relay lens 62, issplit into two light fluxes by a split target plate 63, passes through atwo-hole diaphragm 64, is reflected by a mirror 65, and is reflectedafter an image is formed once on the reflection surface of thereflection rod 67 by a condenser lens 66. Furthermore, the focus lightis reflected at the aperture mirror 21 via the relay lens 20 and animage is formed on the fundus Ef by the object lens 22.

The fundus reflection light of the focus light passes through the sameroute as the cornea reflection light of the alignment light and isdetected by the CCD image sensor 35. A light (split target) captured bythe CCD image sensor 35 is displayed on the display device 3 along withan observation image K. The arithmetic and control unit 200, as in thepast, analyzes the position of the split target, and moves the focusinglens 31 and the focus optical system 60 for focusing. It should be notedthat focusing may be performed manually while visually recognizing thesplit target.

An optical path including a mirror 41, collimator lens 42, and Galvanomirrors 43, 44 is provided behind the dichroic mirror 32. The opticalpath is connected to the OCT unit 100.

The Galvano mirror 44 performs scanning with a signal light LS from theOCT unit 100 in the x-direction. The Galvano mirror 43 performs scanningwith a signal light LS in the y-direction. Scanning may be performedwith the signal light LS in an arbitrary direction in the xy-plane dueto the two Galvano mirrors 43 and 44.

[OCT Unit]

The OCT unit 100 shown in FIG. 2 is provided with an optical system forobtaining a tomo graphic image of the fundus Ef. The optical system hasa similar configuration to a conventional Fourier-Domain-type OCTdevice. That is to say, the optical system is configured to split a lowcoherence light into a reference light and a signal light, make thesignal light propagated through a fundus and the reference lightpropagated through a reference optical path interfere with each other togenerate an interference light, and detects the spectral components ofthis interference light. This detection result (detection signal) istransmitted to the arithmetic and control unit 200.

A light source unit 101 outputs a low coherence light L0. The lowcoherence light L0 is, for example, light (invisible light) consistingof wavelengths that is impossible to be detected by human eyes.Furthermore, the low coherence light L0 is, for example, near-infraredlight having the center wavelength of about 1050-1060 nm. The lightsource unit 101 is configured to include light output device, such as anSLD (super luminescent diode), SOA (Semiconductor Optical Amplifier) andthe like. A light source unit 101 is an example of a “light source” ofthe invention.

The low coherence light L0 output from the light source unit 101 isguided to a fiber coupler 103 by an optical fiber 102 and split intosignal light LS and reference light LR. It should be noted that thefiber coupler 103 acts both as a means to split light (splitter) as wellas a means to synthesize light (coupler), but herein the same isconventionally referred to as a “fiber coupler.”

The signal light LS is guided by the optical fiber 104 and becomes aparallel light flux by a collimator lens unit 105. Furthermore, thesignal light LS is reflected by Galvano mirrors 44 and 43, converged bythe collimator lens 42, reflected by the mirror 41, transmitted througha dichroic mirror 32, and irradiated to the fundus Ef after passingthrough a route that is the same as the light from the LCD 39. Thesignal light LS is scattered and reflected at the fundus Ef. Thescattered light and the reflection light are sometimes all togetherreferred to as the fundus reflection light of the signal light LS. Thefundus reflection light of the signal light LS progresses along the sameroute in the reverse direction and is guided to the fiber coupler 103.

The reference light LR is guided by an optical fiber 106 and becomes aparallel light flux by a collimator lens unit 107. Furthermore, thereference light LR is reflected by mirrors 108, 109, 110, dimmed by anND (Neutral Density) filter 111, and reflected by a mirror 112, with theimage formed on a reflection surface of a reference mirror 114 by acollimator lens 113. The reference light LR reflected by the referencemirror 114 progresses along the same route in the reverse direction andis guided to the fiber coupler 103. It should be noted that an opticalelement for dispersion compensation (pair prism, etc.) and/or an opticalelement for polarization correction (wave plate, etc.) may also beprovided for the optical path (reference optical path) of the referencelight LR.

The fiber coupler 103 superposes the fundus reflection light of thesignal light LS and the reference light LR reflected by the referencemirror 114. Interference light LC thus generated is guided by an opticalfiber 115 and output from an exit end 116. Furthermore, the interferencelight LC is converted to a parallel light flux by a collimator lens 117,spectrally divided (spectrally decomposed) by a diffraction grating 118,converged by the convergence lens 119, and projected onto the lightreceiving surface of a CCD image sensor 120.

The CCD image sensor 120 is for example a line sensor, and detects therespective spectral components of the spectrally decomposed interferencelight LC and converts the components into electric charges. The CCDimage sensor 120 accumulates these electric charges and generates adetection signal. Furthermore, the CCD image sensor 120 transmits thedetection signal to the arithmetic and control unit 200.

Although a Michelson-type interferometer is employed in this embodiment,it is possible to employ any type of interferometer such as aMach-Zehnder-type as necessary. Instead of a CCD image sensor, othertypes of image sensors, such as a CMOS (Complementary Metal OxideSemiconductor) image sensor, can be used.

[Arithmetic and Control Unit]

A configuration of the arithmetic and control unit 200 will bedescribed. The arithmetic and control unit 200 analyzes the detectionsignals inputted from the CCD image sensor 120, and forms an OCT imageof the fundus Ef. An arithmetic process for this is the same as that ofa conventional Fourier-Domain-type OCT device.

Further, the arithmetic and control unit 200 controls each part of theretinal camera unit 2, the display device 3 and the OCT unit 100.

As control of the retinal camera unit 2, the arithmetic and control unit200 executes: control of action of the observation light source 101, theimaging light source 103 and LED's 51 and 61; control of action of theLCD 39; control of movement of the focusing lens 31; control of movementof the reflection rod 67; control of movement of the focus opticalsystem 60; control of action of the respective Galvano mirrors 43 and44; and so on.

Further, as control of the OCT unit 100, the arithmetic and control unit200 executes: control of action of the light source unit 101; control ofmovement of the reference mirror 114 and the collimator lens 113;control of action of the CCD image sensor 120; and so on.

The arithmetic and control unit 200 includes a microprocessor, a RAM, aROM, a hard disk drive, a communication interface, and so on, as inconventional computers. The storage device such as the hard disk drivestores a computer program for controlling the fundus observationapparatus 1. The arithmetic and control unit 200 may be provided with acircuit board dedicated for forming OCT images based on detectionsignals from the CCD image sensor 120. Moreover, the arithmetic andcontrol unit 200 may be provided with operation devices (input devices)such as a keyboard and a mouse, and/or display devices such as LCD.

The retinal camera unit 2, display device 3, OCT unit 100, andarithmetic and control unit 200 may be integrally configured (that is,within a single case), or configured as separate bodies.

[Input Device]

The input device 300 is used in order for the subject to respond duringthe eyesight measurement. In the eyesight measurement, a predeterminedvisual target for measuring eyesight is projected onto the eye E. Thesubject inputs the result of visual confirmation of this target usingthe input device 300. For example, when a Landolt ring is used as atarget, the subject inputs the direction of the rift in the Landolt ringusing the input device 300.

The input device 300 is configured, for example, to include a joy sticksuch as the one shown in FIG. 3. The subject tilts the joystick in thedirection corresponding to the result of visual confirmation to thetarget. The input device 300 transmits an electrical signalcorresponding to this operation content (tilting direction) to thearithmetic control unit 200. The input device 300 is one example of the“operation part” of the invention.

[Control System]

A configuration of a control system of the fundus observation apparatus1 will be described with reference to FIG. 3.

(Controller)

The control system of the fundus observation apparatus 1 has aconfiguration centered on a controller 210 of the arithmetic and controlunit 200. The controller 210 includes, for example, the aforementionedmicroprocessor, RAM, ROM, hard disk drive, and communication interface.The controller 210 is an example of a “controlling part” of theinvention.

A controller 210 is provided with a main controller 211, storage 212 anda target setting part 214. The main controller 211 performs theaforementioned various kinds of control. Specifically, the maincontroller 211 controls a scan driver 70 as well as a focus driver 80 ofthe retinal camera unit 2, and further controls a reference driver 130of the OCT unit 100.

The scan driver 70 is configured, for example, including a servo motorand independently changes the facing direction of the Galvano mirrors 43and 44. The scan driver 70 consists of one example of the “scanningpart” in the invention along with the Galvano mirrors 43 and 44.

The focus driver 80 is configured, for example, including a pulse motorand moves the focusing lens 31 in the optical axis direction. Thereby,the focus position of light towards the fundus Ef is changed.

The reference driver 130 is configured, for example, including a pulsemotor and integrally moves the collimator lens 113 as well as thereference mirror 114 along the travelling direction of the referencelight LR.

The main controller 211 executes a process of writing data into thestorage 212, and a process of reading out the data from the storage 212.

The storage 212 stores various kinds of data. The data stored in thestorage 212 is, for example, image data of OCT images, image data offundus images, and eye information. The eye information includesinformation on the eye, for example, information on a subject such as apatient ID and a name, information on identification of left eye orright eye, and so on.

Moreover, the eyesight value of the eye E measured by the fundusobservation apparatus 1 is stored in the storage 212. Although thedetails will be described later, this eyesight value is stored incorrelation with the OCT image. The storage 212 is one example of the“storage part” of the invention.

It should be noted that the storage part is not limited to storagedevices such as hard disk drives and RAM, and may be any recording mediawritable by a drive device. As this recording media, for example,optical disks, magnetic optical disks (such as CD-R/DVD-RAM/MO),magnetic recording media (such as floppy Disks®/ZIP), SSDs (Solid StateDrives), etc. may also be used.

Moreover, OCT images and eyesight values may be transmitted to thepredetermined storage part to be stored via a network such as theInternet and LAN. Furthermore, it is not necessary to store OCT imagesand eyesight values in the same storage device, and they may be storedin separate storage devices. It should be noted that also in this case,the OCT images and the eyesight values must be correlated with eachother.

Furthermore, target size adjustment information 213 is preliminarilystored in the storage 212. The target size adjustment information 213includes the information that associates the position of the focusinglens 31 with the target size. Hereinafter, the target size adjustmentinformation 213 is described in detail.

In this embodiment, eyesight measurement is conducted on the eye E byprojecting the visual target for measuring eyesight displayed on the LCD39 to the fundus Ef. The eyesight examination is for determining theeyesight values based on the target size that can be visually confirmed.(As a specific example, the eyesight values are determined by presentingvarious sizes of Landolt rings to the eye E, obtaining a responseregarding the direction of the rift in the presented Landolt ring, andthen determining whether the response is true or false.)

However, in the configuration in which the target displayed on the LCD39 is projected on the fundus Ef, even if the size of the targetdisplayed on the LCD 39 is the same, the size of the image projected onthe fundus Ef may be different due to the eye refractive power of theeye E. Consequently, the accuracy of the eyesight examination islowered.

The target adjustment information 213 is referenced in order to avoid adecrease in measurement accuracy due to such a difference in eyerefractive power. In this embodiment, as described above, focusing ofthe optical system on the fundus Ef is accomplished by projecting asplit target on the fundus Ef using the focus optical system 60 andmoving the focusing lens 31 and the focus optical system 60 based on theposition of the split target. The position of the split target isaffected by the eye refractive power of the eye E, i.e., the refractivepower of the cornea and the lens.

The target size adjustment information 213 includes, as information formaking the projection size of the visual target for measuring eyesightonto the fundus independent of the eye refractive power, informationthat correlates the position of the focusing lens 31 and the size of thevisual target for measuring eyesight. For example, informationcorrelating, for the target at each eyesight value, the position of thefocusing lens 31 and the display size of the target on the LCD 39 isrecorded in the target size adjustment information 213. This informationis in the form of a table, graph, mathematical expression, etc.

This information may be created by, for example, a numerical simulationsuch as a ray trace. Moreover, this information may also be created byactually performing a measurement using an eye model, an eye on a livingbody or an isolated eye.

It should be noted that the information recorded in the target sizeadjustment information 213 is not limited to the above. For example,each position of the focusing lens 31 may be correlated with the displaysize of the target for each eyesight value.

Moreover, the information recorded in the target size adjustmentinformation 213 may be information that correlates the position of thefocus optical system 60 and the target size. Here, the focus opticalsystem 60 and the focusing lens 31 are moved in conjunction with eachother, with the position of the focus optical system 60 having aone-on-one correspondence with the position of the focusing lens 31.Therefore, this modification example can be considered equivalent to thecase in which the position of the focusing lens 31 and the target sizeare correlated.

Moreover, the information recorded in the target size adjustmentinformation 213 may be the information that correlates the eyerefractive power value and the target size. In this case, the eyerefractive power value of the eye E that is previously acquired isinput, and the target size is adjusted based on the input value. Here,since the eye refractive power value corresponds one-on-one with theposition of the focusing lens 31 (at least theoretically), thismodification example can also be considered equivalent to the case inwhich the position of the focusing lens 31 and the target size arecorrelated.

The target setting part 214 executes various setting processes regardingthe target projected on the eye E, such as a visual target for measuringeyesight and a fixation target. The target setting part 214 is providedwith a target size setting part 215, a fixation target setting part 216and an eyesight value determination part 217.

The target size setting part 215 acquires the position information ofthe focusing lens 31 and obtains the size of the visual target formeasuring eyesight based on the position information and the target sizeadjustment information 213.

An example of a process for acquiring the position information of thefocusing lens 31 is described. The focusing lens 31 is, as describedabove, moved by the focus drive 80 based on the control by the maincontroller 211. Consequently, based on the control content (controlhistory) by the main controller 211, the position information of thefocusing lens 31 can be acquired. More specifically, when the focusdrive 80 includes a pulse motor, the position information of thefocusing lens 31 can be acquired with reference to the pulse numbertransmitted from the main controller 211 to the focus drive 80.Moreover, it is also possible to use a detector (for example, apotentiometer) that detects the position of the focusing lens 31.

Upon acquisition of the position information of the focusing lens 31,the target size setting part 215 obtains the target size correspondingto that position information with reference to the target sizeadjustment information 213.

The fixation target setting part 216 performs setting regarding thefixation target displayed on the LCD 39. Specifically, the fixationtarget setting part 216 sets the display position of the fixation targeton the LCD 39. For example, the fixation target setting part 216 setsthe display position of the fixation target on the LCD 39 based on theregion for scanning with signal light LS (scanning region; describedlater) using Galvano mirrors 43, 44. The operational example of thefixation target setting part 216 will be described later.

The eyesight value determination part 217 executes various processes forobtaining the eyesight value of the eye E. As these processes, forexample, conventional approaches are applicable in which the visualtargets for measuring eyesight corresponding to various eyesight valuesare automatically switched to be presented to the eye. (For example, seerepublished No. 03/041571.) Hereinafter, an operational example of theeyesight value determination part 217 is described.

First, the eyesight value determination part 217 determines the visualtarget for measuring eyesight to be first presented to the eye E. As atarget to be first presented, a target corresponding to thepredetermined eyesight value is selected. This first target is a targetcorresponding to, for example, the eyesight value 0.1.

Moreover, when previously measured eyesight values can be acquired forthis eye E, the first target can be determined based on thisinformation. For example, when the previously obtained eyesight valuefor the above eye E is 0.7, a target corresponding to an eyesight valuelower than that value (for example, 0.5) by a predetermined value isselected as the first target.

Previous eyesight values may be input using, for example, the operationpart 250, or may be obtained from, for example, an electronic medicalrecord system through, for example, LAN. Moreover, previous eyesightvalues can be correlated to the above-mentioned information on the eyeand stored in the storage 212. In addition, the previous eyesight valuereferenced in this examination is preferably the newest among thepreviously measured eyesight values. When the previous eyesight value isobtained from the electric medical record system, it is possible toselectively obtain the newest eyesight value with reference to themedical examination date recorded in the electric medical records.

Furthermore, the eyesight value determination part 217 determines thetarget to be presented next, based on the response to the targetpresented to the eye E from the subject. For this process, for example,the same process as the conventional process can be used. For example,if a correct answer is obtained twice for targets with a certaineyesight value, then a target with the next higher eyesight value isselected. In contrast, if a wrong answer is obtained twice for targetswith a certain eyesight value, then a target with the next lowereyesight value is selected.

Furthermore, the eyesight value determination part 217 determines theeyesight value of the eye E based on the response content from thesubject according to the change in the target size. This process is, forexample, executed similarly to the conventional process. For example, ifa correct answer is obtained twice for targets with a certain eyesightvalue, and a wrong answer is obtained twice for targets with a nexthigher eyesight value, then the former certain eyesight value isdetermined as the eyesight value for the eye E. Moreover, if a correctanswer is obtained twice for targets at the highest presentable eyesightvalue (for example, 2.0), that highest eyesight value is determined asthe eyesight value for the eye E. Furthermore, if a wrong answer isobtained twice for targets with the lowest presentable eyesight value(for example, 0.1), the result is that the eyesight value isunmeasurable or less than a predetermined value.

The target setting part 214 may be configured such that it can set thedisplay position of the visual target for measuring eyesight on the LCD39.

(Image Forming Part)

An image forming part 220 forms image data of a tomographic image of thefundus Ef based on the detection signals from the CCD image sensor 120.Like the conventional Fourier-Domain OCT, this process includesprocesses such as noise elimination (noise reduction), filtering, andFFT (Fast Fourier Transform).

The image forming part 220 includes, for example, the aforementionedcircuit board and communication interface. It should be noted that“image data” and the “image” presented based on the image data may beidentified with each other in this specification.

(Image Processor)

An image processor 230 executes various image processing and analysis onimages formed by the image forming part 220. For example, the imageprocessor 230 executes various correction processes such as luminancecorrection and dispersion correction of images.

Further, the image processor 230 executes, for example, an interpolationprocess of interpolating pixels between tomographic images formed by theimage forming part 220, thereby forming image data of athree-dimensional image of the fundus Ef.

Image data of a three-dimensional image refers to image data that thepositions of pixels are defined by the three-dimensional coordinates.The image data of a three-dimensional image is, for example, image datacomposed of three-dimensionally arranged voxels. This image data isreferred to as volume data, voxel data, or the like. For displaying animage based on the volume data, the image processor 230 executes arendering process (such as volume rendering and MIP (Maximum IntensityProjection)) on this volume data, and forms image data of a pseudothree-dimensional image taken from a specific view direction. On adisplay device such as the display 240, this pseudo three-dimensionalimage is displayed.

Further, it is also possible to form stack data of a plurality oftomographic images as the image data of a three-dimensional image. Stackdata is image data obtained by three-dimensionally arranging a pluralityof tomographic images obtained along a plurality of scanning lines,based on the positional relation of the scanning lines. That is to say,stack data is image data obtained by expressing a plurality oftomographic images defined by originally individual two-dimensionalcoordinate systems by a three-dimensional coordinate system (namely,embedding into a three-dimensional space).

The image processor 230 includes, for example, the aforementionedmicroprocessor, RAM, ROM, hard disk drive, circuit board, and so on.

The image forming part 220 (and the image processor 230) is an exampleof the “image forming part” of the invention.

(Display and Operation Part)

The display 240 is configured including a display device of theaforementioned arithmetic and control unit 200. The operation part 250is configured including an operation device of the aforementionedarithmetic and control unit 200. Furthermore, the operation part 250 mayalso include various kinds of buttons or keys provided with the case ofthe fundus observation apparatus 1 or its outside. For example, if theretinal camera unit 2 has a case that is the same as conventional funduscameras, a joy stick, operation panel, etc. provided with the case mayalso be included in the operation part 250. Furthermore, the display 240may also include various display devices such as a touch panel monitor,etc. provided with the case of the retinal camera unit 2.

The display 240 and the operation part 250 do not need to be composed asseparate devices. For example, like a touch panel LCD, a device in whichthe display function and the operation function are integrated can beused.

[Scan with Signal Light and OCT Image]

A scan with the signal light LS and an OCT image will be described.

The scan aspect of the signal light LS by the fundus observationapparatus 1 is, for example, a horizontal scan, vertical scan, cruciformscan, radial scan, circular scan, concentric scan, and helical scan.These scan aspects are selectively used as necessary in consideration ofan observation site of the fundus, an analysis target (the retinalthickness or the like), a time required to scan, the accuracy of a scan,and so on.

A horizontal scan is a scan with the signal light LS in the horizontaldirection (x-direction). The horizontal scan includes an aspect ofscanning with the signal light LS along a plurality of scanning linesextending in the horizontal direction arranged in the vertical direction(y-direction). In this aspect, it is possible to set any intervalbetween scanning lines. By setting the interval between adjacentscanning lines to be sufficiently narrow, it is possible to form theaforementioned three-dimensional image (three-dimensional scan). Avertical scan is also performed in a similar manner.

A cruciform scan is a scan with the signal light LS along a cross-shapetrajectory formed by two linear trajectories (line trajectories)orthogonal to each other. A radial scan is a scan with the signal lightLS along a radial trajectory formed by a plurality of line trajectoriesarranged at predetermined angles. The cruciform scan is an example ofthe radial scan.

A circular scan is a scan with the signal light LS along a circulartrajectory. A concentric scan is a scan with the signal light LS along aplurality of circular trajectories arranged concentrically around apredetermined center position. The circular scan is regarded as aspecial example of the concentric scan. A helical scan is a scan withthe signal light LS along a helical trajectory while making the turningradius gradually smaller (or greater).

With the configuration as described before, the Galvano mirrors 43 and44 are capable of scanning with the signal light LS in the x-directionand the y-direction independently, and is therefore capable of scanningwith the signal light LS along an arbitrary trajectory on the xy-plane.Thus, it is possible to realize various types of scan aspects asdescribed above.

By scanning the signal light LS in the mode described above, it ispossible to form tomographic images of the depthwise direction(z-direction) along scanning lines (scan trajectory). Moreover, in acase that the interval between scanning lines is narrow, it is possibleto form the aforementioned three-dimensional image.

A region on the fundus Ef subjected to scanning by the signal light LSas above is referred to as a scanning region. For example, a scanningregion in three-dimensional scanning is a rectangular-shaped region inwhich a plurality of horizontal scans are arranged. Furthermore, ascanning region in a concentric circular scan is a disc-shaped regionsurrounded by the trajectories of a circular scan of a maximum diameter.Moreover, the scanning region in a radial scan is a disc-shaped (orpolygonal-shaped) region linking end positions of scanning lines.

[Operation]

The operation of the fundus observation apparatus 1 is described. Theflow chart shown in FIG. 4 represents an example of the operation of thefundus observation apparatus 1.

First, as in the conventional manner, the main controller 211 controls,for example, the alignment optical system 50 to perform alignment to theeye E, and also controls, for example, the focus optical system 60, thefocus drive 80, etc., to perform focusing on the fundus Ef (S1).

Next, the main controller 211 adjusts the position of the referencemirror 114 (as well as the position of the collimator lens 113) toadjust the interference state of the signal light LS and the referencelight LR (S2). At this time, adjustment is made so that the image of thedesired depthwise position of the fundus Ef becomes clear. Moreover, itis desirable to adjust the position of the reference mirror 114 so thatthe image of the predetermined depthwise position (for example, theretina surface) is located within a predetermined range in the frame. Itshould be noted that the position adjustment of the reference mirror 114may be manually performed using the operation part 250 or may beautomatically performed.

Upon completion of the adjustment of the interference state, thefixation target setting part 216 sets the display position of thefixation target on the LCD 39 corresponding to the predeterminedscanning region (for example, a rectangular region for three-dimensionalscanning) (S3). It should be noted that the scanning region is set, forexample, before or after step 1.

Furthermore, the fixation target setting part 215 adjusts the size ofthe visual target for measuring eyesight based on the position of thefocusing lens 31, which is moved during focusing in step 1, and thetarget size adjustment information 213 (S4).

The main controller 211 controls the LCD 39 to display the fixationtarget in the display position set in step 3 and fixate the eye E (S5).Furthermore, the main controller 211 allows the first visual target formeasuring eyesight, of which the size has been adjusted in step 4, to bedisplayed on the LCD 39, and begins the eyesight measurement (S6). Thiseyesight measurement is for measuring the eyesight at the position onthe fundus Ef (i.e., projection position of the fixation target)corresponding to this fixation position.

In this operational example, as shown in FIG. 5, the fixation target Vis displayed in the central position of the display screen of the LCD39, and the Landolt ring T is displayed such that the central positionof the Landolt ring T matches the position of the fixation target V.

At the same time as the start of the eyesight examination, the maincontroller 211 controls the light source unit 101 and the Galvanomirrors 43 and 44 to begin the measurement in the predetermined scanningregion (for example, three-dimensional scanning) (S7).

The positional relationship between the scanning region of the signallight LS and the target projection region on the fundus Ef is shown inFIG. 6. In this operational example, as in the FIG. 5, the fixationtarget V is projected on the central position of the projection regionof the Landolt ring T, and furthermore, the projection region of thefixation target V is matched to the central position of the scanningregion R (rectangular region). It should be noted that the fixationtarget displayed on the LCD 39 and the projected image of this fixationtarget on the fundus Ef are denoted by the same symbol V, and theLandolt ring displayed on the LCD 39 and the projected image of thisLandolt ring on the fundus Ef are denoted by the same symbol T.

Such a projection mode is achieved, for example, as follows. First, thecentral position of the display screen of the LCD 39 is placed on anoptical axis of the imaging optical system 30. Moreover, the scanningregion R is set such that its central position is located on the opticalaxis of the imaging optical system 30. Therefore, by displaying thefixation target V in the central position of the display screen of theLCD 39 and setting this scanning region R as such, the central positionof the scanning region R is matched to the projection region of thefixation target V (i.e., both are placed on the extended line of theoptical axis). Furthermore, since the Landolt ring T is displayed on theLCD 39 such that its central position is placed in the central positionof the display screen, the central position of the Landolt ring T, theprojection region of the fixation target V and the central position ofthe scanning region R are matched on the fundus Ef.

The controller 210 executes the eyesight measurement at the position ofthe fundus Ef projected with the fixation target V while scanning thescanning region R with the signal light LS. At this time, the signallight LS is used to sequentially scan a plurality of lines of horizontalscanning (scanning lines) included in the three-dimensional scanning.Then, the image forming part 220 forms a tomographic image correspondingto each scanning line based on the detection results of interferencelight LC of the signal light LS and the reference light LR (S8).Tomographic images that are formed sequentially are stored in thestorage 212 while being correlated with position information ofcorresponding scanning line (scanning position information). Thescanning position information is, for example, information based on thecontrol to the scan drive 70 (i.e., the direction of the Galvano mirrors43, 44). When the scanning along all scanning lines is completed, thescanning may be ended or similar scanning may be executed again. Here,the eyesight measurement is executed by the eyesight value determinationpart 217 in the manner described above.

When the eyesight value is obtained by the eyesight value determinationpart 217 (S9), the main controller 211 selects a tomographic imagecorresponding to the scanning line closest to the eyesight measurementposition (the position projected with the fixation target V) (S10), andstores this tomographic image and the eyesight value in the storage 212while correlating them with each other (S11). Here, the selectionprocess of the tomographic image is executed with reference to theabove-mentioned scanning position information.

The main controller 211 allows the tomographic image and the eyesightvalue to be displayed on the display device 3 (or the display 240) (S12). Consequently, the examiner can observe the tomographic image of thefundus Ef at the eyesight measurement position.

In this operational example, examination at the fixation position isconducted as described above. Therefore, for the eye E that has nodisorder in the macula flava (including a healthy eye), the eyesightvalue and the tomographic image in the macula flava are generallyobtained. On the other hand, for the eye E that has, for example, adisorder in the macula flava, the fixation target V tends to be viewedby the site having the highest visual ability in the fundus Ef (otherthan the macula flava), so the eyesight value and the tomographic imagein such a site are generally obtained.

Instead of conducting an examination on the fixation position in thisway, it is also possible to conduct an examination on the site ofinterest (treatment site, diagnosed site, etc.) other than the fixationposition. To this end, as described in detail in the followingoperational example, it is effective to conduct an examination under thecondition that the display position of the fixation target V is shiftedfrom the display position of the visual target for measuring eyesight onthe LCD 39.

Another Operational Example

In this operational example, eyesight measurement is conducted onvarious positions in the fundus Ef by changing the relative position ofthe projection region of the visual target for measuring eyesight andthe projection region of the fixation target, and furthermore, atomographic image covering the eyesight measurement position isobtained. Hereinafter, the operational example shown in the flowchartshown in FIG. 7 is described.

As a preliminary stage of the examination, as in the operational exampledescribed above, the alignment, focusing, determination of the scanningregion, and adjustment of the interference state are performed (S21).

The fixation target setting part 216 sets the display position of thefixation target on the LCD 39 corresponding to the scanning region (forexample, a rectangular region for three-dimensional scanning) (S22).Moreover, the target setting part 214 sets the display position of thevisual target for measuring eyesight on the LCD 39 (S23). Furthermore,the target size setting part 215 adjusts the size of the visual targetfor measuring eyesight based on the position of the focusing lens 31after focusing and the target size adjustment information 213 (S24).

It should be noted that, in this operational example, as opposed to thecase shown in FIG. 5, it is not necessary to display the fixation targeton the central position of the display screen, and furthermore, it isnot necessary to match the central position of the visual target formeasuring eyesight to the position of the fixation target. For example,as shown in FIG. 8, the fixation target V is displayed in a positiondeviating from the central position of the display screen of the LCD 39,and the Landolt ring T is displayed with its central position deviatingfrom the position of the fixation target V. It should be noted that, inthe example shown in FIG. 8, the display positions of the fixationtarget V and the Landolt ring T both deviate from the central positionof the display screen, but one of these positions may be displayed inthis central position while the other is displayed in other positions.

The important point here is that the fixation target V and the Landoltring T are displayed in different positions. Specifically, when thefixation target V and the Landolt ring T are displayed in differentpositions, on the assumption that the eye E is fixed by the fixationtarget V, the eyesight in the position on the fundus Ef that isdifferent from the fixation position can be measured. (In the aboveoperational example, the eyesight in the fixation position is measured.)Moreover, by changing the relative position of the fixation target V andthe Landolt ring T, eyesight in various positions on the fundus Ef canbe measured.

The main controller 211 controls the LCD 39 to display the fixationtarget in the display position set in step 22 and fix the eye E (S25).Furthermore, the main controller 211 controls the LCD 39 to display thefirst visual target for measuring eyesight in the display position setin step 23, and begins the eyesight measurement (S26).

At the same time as the start of the eyesight measurement, the maincontroller 211 begins the measurement in the scanning region (forexample, three-dimensional scanning) (S27).

The positional relationship between the scanning region of the signallight LS and the target projection region on the fundus Ef is shown inFIG. 9. In this operational example, as in FIG. 8, the fixation target Vand the Landolt ring T are projected at different positions. Moreover,as in the operational example described above (FIG. 6), the scanningregion R is set such that its central position is located on the opticalaxis of the imaging optical system 30. Consequently, the fixation targetV and the Landolt ring T are projected at a position different from thecentral position of the scanning region R. It should be noted that, asdescribed above, when the fixation target V or the Landolt ring T isdisplayed at the central position of the display screen of the LCD 39,the target displayed at this central position is projected at thecentral position of the scanning region R.

The controller 210 executes the eyesight measurement on the position ofthe fundus Ef projected with the Landolt ring T while scanning thescanning region R with the signal light LS. At this time, the signallight LS is used to sequentially scan a plurality of scanning linesincluded in the three-dimensional scanning. The image forming part 220forms a tomographic image corresponding to each scanning line (S28).Tomographic images that are formed sequentially are stored in thestorage 212 while being correlated with the scanning positioninformation. The scanning position information is, for example,information based on the control to the scan drive 70 (i.e., thedirection of the Galvano mirrors 43, 44). When the scanning along allscanning lines is completed, the scanning may be ended or similarscanning may be executed again. Here, the eyesight measurement isexecuted by the eyesight value determination part 217 in the mannerdescribed above.

When the eyesight value of this measurement position is obtained (S29),the main controller 211 selects a tomographic image corresponding to thescanning line closest to the eyesight measurement position (S30), andstores the measurement position, the tomographic image and the eyesightvalue in the storage 212 while correlating them with each other (S31).Here, the correlation of the tomographic image and the eyesight valuecan be achieved similarly to the above operational example. Moreover,the measurement position can be determined based on, for example, therelative position of the fixation target V and the Landolt ring T (therelative position of both display positions).

If the examination is not completed at all the measurement positions(S32: No), the target setting part 214 sets the display positions of thefixation target V and the Landolt ring T on the LCD 39 corresponding tothe next measurement position. The main controller 211 allows thefixation target V and the Landolt ring T to be displayed at the setdisplay positions. Consequently, each projection region of the fixationtarget V and the Landolt ring T on the fundus Ef is changed. Under thecondition that the eye E is fixed by this fixation target V, the Landoltring T is projected at the next measurement position described above(S33). Then, the eyesight measurement at this new measurement positionis started (S26). At this time, scanning with the signal light LS may beexecuted again (S27).

It should be noted that, when the new measurement position deviates fromthe prior scanning region R, the controller 210 newly sets the scanningregion to include the new measurement position (i.e., so that a newprojection region of the Landolt ring T is overlapped), and performsscanning with the signal light LS to form a tomographic image.

The change in the measurement position as described above is, forexample, sequentially executed for a predetermined number of positions.As a specific example, the eyesight measurement is first conducted onthe central position of the scanning region R as shown in FIG. 6, andthen the eyesight measurement is further conducted on each apex positionof a rectangle enclosing this central position.

Moreover, it is also possible to set the measurement position based onthe condition of the eye E. For example, it is also possible to set thesite of interest and its peripheral position of the eye E as themeasurement position. Such a measurement position can be set based on,for example, the positional relationship of the site of interestrelative to the macular area. Moreover, this positional relationship canbe obtained based on, for example, the fundus image. In addition, it isalso possible to set the measurement position so as to avoid the regionon the fundus Ef that is thought to have low eyesight (for example, aregion affected due to cataracts, a region that has an untreatableretinal disease, etc.)

When the examination of all measurement positions is completed (S32:Yes), the main controller 211 selects the highest value among theacquired eyesight values (S34). The main controller 211 allows theselected eyesight value and the measurement position and tomographicimage correlated to this eyesight value to be displayed on the displaydevice 3 (or the display 240) (S35). Consequently, the examiner canrecognize the site having good eyesight on the fundus Ef, andfurthermore, can observe the tomographic image of the fundus Ef at thissite.

When such an examination is applied at follow-ups, the measurementposition in which the highest eyesight value is obtained may be changed.For example, in the follow-ups after the treatment of the disease in themacula flava, the highest eyesight value is obtained first at a siteother than the macula flava, and then, in the course of treatment, thehighest eyesight value may be obtained in the macula flava. In this way,therapeutic effect may appear not only as the improvement of theeyesight value, but also the change in the measurement position in whichthe highest eyesight value is obtained. Moreover, it is also possible tospecify the measurement position at which the highest eyesight value isobtained as an actual fixation position.

Actions and Effects

The actions and effects of the fundus observation apparatus 1 asdescribed above will be described.

According to the fundus observation apparatus 1, it is possible toexecute the OCT measurement and the eyesight measurement whilesuperposing the scanning region R of the signal light LS on theprojection region of the visual target for measuring eyesight (Landoltring T) to form the tomographic image of the fundus Ef at the scanningregion R, and it is also possible to store the eyesight value measuredusing the Landolt ring T and the tomographic image while correlatingthem to each other.

Here, the fundus observation apparatus 1 controls the LCD 39 based onthe scanning region R of the signal light LS to superpose the projectionregion of the Landolt ring T on the fundus Ef on the scanning region R.Furthermore, the fundus observation apparatus 1 can display the fixationtarget V on the LCD 39 along with the Landolt ring T to project them onthe fundus Ef, and changes the projection region of the Landolt ring Ton the fundus Ef by changing the relative display position of theLandolt ring T and the fixation target V based on the scanning region R.

According to such the fundus observation apparatus 1, it is possible toacquire an image (tomographic image) of the eyesight measurement site inthe fundus Ef. In particular, when the projection region and thescanning region are set to include a site of interest in the fundus Ef,the tomographic image and the eyesight value of that site of interestcan be acquired. Consequently, the condition of the eyesight and themorphology of the retina, etc., can be recognized, and furthermore,their relationship can also be recognized.

For example, even if the morphology of the retina is improved, thepatient cannot realize the therapeutic effect unless the eyesight isimproved. By using the fundus observation apparatus 1, it is possible toclosely investigate whether or not such a situation has occurred.

Moreover, the fundus observation apparatus 1 allows different sizes ofvisual targets for measuring eyesight to be displayed on the LCD 39 tochange the size of the projection region on the fundus Ef, therebymaking it possible to project the visual target for measuring eyesightcorresponding to different eyesight values on the fundus Ef. It shouldbe noted that the size of the projection region on the fundus Ef canalso be changed with a target of the same size being displayed byproviding an optical element such as a lens between the LCD 39 and theeye E.

Furthermore, the fundus observation apparatus 1 can adjust the size ofthe visual target for measuring eyesight displayed on the LCD 39 basedon the position of the focusing lens 31. It should be noted that, inplace of adjusting the display size, the size of the projection regionmay be changed by the optical element described above.

With such a configuration, it is possible to precisely measure theeyesight value without being affected by the eye refractive power of theeye E.

Moreover, the fundus observation apparatus 1 is configured to change thesize of the visual target for measuring eyesight displayed on the LCD 39based on the response contents from the subject against the visualtarget for measuring eyesight presented to the eye E, and furthermore,to determine the eyesight value of the eye E based on the responsecontents according to the change of the visual target for measuringeyesight.

With such a configuration, it is possible to automatically measure theeyesight at a predetermined site in the eye E (macula flava, site ofinterest, etc.).

Moreover, the low-coherence light L0 used in the OCT measurement by thefundus observation apparatus 1 is preferably invisible light. By usingsuch invisible light, even when the eyesight measurement and the OCTmeasurement are conducted simultaneously, the signal light LS is notvisually recognized by the subject. Consequently, the complexity in theexamination can be reduced and the examination can be smoothlyconducted, thereby further improving the accuracy and precision of theexamination results. It should be noted that it is necessary for thesubject to visually confirm the fixation target and the visual targetfor measuring eyesight.

Furthermore, the invisible light used in the OCT measurement ispreferably near-infrared light of center wavelength within the rangefrom about 1050 to 1060 nm. Here, if the center wavelength is shorterthan 1050 nm, there is a risk that the signal light LS may not certainlyreach the fundus Ef. On the other hand, if the center wavelength islonger than 1060 nm, there is a risk that the signal light LS will beabsorbed by the water content within the eyeball so that it may notcertainly reach the fundus Ef.

The configuration described above is merely one example for favorablyimplementing the present invention. Therefore, it is possible toproperly make arbitrary modification within the scope of the presentinvention.

In the above embodiment, the configuration in which the projectionregion of the visual target for measuring eyesight on the fundus issuperposed on the scanning region by controlling the display part basedon the scanning region of the signal light, but it is also possible toapply a configuration for performing the opposite process. Specifically,it is possible to apply a configuration in which the scanning region ofthe signal light on the fundus is superposed on the projection region ofthe visual target for measuring eyesight by controlling the scanningpart based on the display position of the visual target for measuringeyesight on the display part.

Such a configuration is shown in FIG. 10. It should be noted that theretinal camera unit 2 and the OCT unit 100 have the same configurationas that in the above embodiment (refer to FIG. 1, FIG. 2).

Moreover, it is possible to apply various configurations described inthe above embodiments to this modification example. For example, it ispossible to apply the configuration in which the visual targets formeasuring eyesight corresponding to various eyesight values ispresented, the configuration in which the size of the visual target formeasuring eyesight is adjusted, the configuration in which the eyesightvalue is automatically obtained, the configuration for the light source,etc.

The block diagram shown in FIG. 10 is almost the same as that shown inFIG. 3. However, it is different from the configuration in FIG. 3 inthat the controller 210 of this modification example is provided with ascan setting part 218 and in that the fixation target setting part 216is not provided. It should be noted that the fixation target settingpart 216 may also be provided in this modification example.

The scan setting part 218 performs setting in regard to scanning withthe signal light LS. Specifically, the scan setting part 218 sets thescanning region of the signal light LS by the Galvano mirrors 43, 44.For example, the scan setting part 218 sets the scanning region based onthe display position of the visual target for measuring eyesight on theLCD 39 so that the projection region of the visual target for measuringeyesight and the scanning region are overlapped with each other.

An operation example of the scan setting part 218 is described. Thedisplay position of the visual target for measuring eyesight on the LCD39 can be recognized by the main controller 211 because it is controlledby the main controller 211. For example, when the central position ofthe display screen of the LCD 39 is located on an optical axis of theimaging optical system 30, the display position of the target can berecognized as a displacement of the central position of the targetrelative to the central position of the display screen. Moreover, thedisplay region of the target on the display screen can be recognizedbased on the display size of the target.

Furthermore, the direction of each of the Galvano mirrors 43, 44 can berecognized by the main controller 211. Specifically, the main controller211 can recognize the position (reference position) of each Galvanomirror 43, 44 for directing the signal light LS such that it is guidedin a direction parallel with the optical axis.

Moreover, the scanning mode of the signal light LS (three-dimensionalscanning, radial scanning, etc.) is selected beforehand, and the scansetting part 218 sets the position of the scanning region in theselected scanning mode based on the display position of the target.

When achieving the condition shown in FIG. 6, since the Landolt ring Tand the fixation target V are displayed on the optical axis, the scansetting part 218 sets a rectangular scanning region R centered on thereference position of the Galvano mirrors 43, 44. The main controller211 allows the Landolt ring T and the fixation target V to be displayedat the central position of the LCD 39, and also controls the scan drive70 to sequentially scan with the signal light LS along a plurality ofscanning lines included in the set scanning region R. Consequently, asshown in FIG. 6, it is possible to conduct the examination with thescanning region R and the Landolt ring T overlapped with each other.

Moreover, when achieving the condition shown in FIG. 9, since theLandolt ring T and the fixation target V are displayed at any positionon the display screen, the scan setting part 218 sets the scanningregion R (i.e., the driving range of the Galvano mirrors 43, 44) so thatit is superposed on the projection region of the Landolt ring T based onthe display position of the Landolt ring T. The main controller 211allows the Landolt ring T and the fixation target V to be displayed onthe LCD 39, and also controls the scan drive 70 to sequentially scanwith the signal light LS along a plurality of scanning lines included inthe set scanning region R. Consequently, as shown in FIG. 9, it ispossible to conduct the examination with the scanning region R and theLandolt ring T overlapped with each other.

According to such a modification example, it is possible to acquire animage of the eyesight measurement site in the fundus Ef. It should benoted that in the above embodiment the examination is conducted bysetting the projection region of the target superposed on thepreliminarily set scanning region, but in this modification example,conversely, the examination can be conducted by setting the scanningregion superposed on the preliminarily set projection region of thetarget.

In the above embodiment, the Landolt ring is used as the visual targetfor measuring eyesight, but it is possible to apply various targetsother than this. For example, the target pattern can be changed such asby displaying various characters. Moreover, the target is not limited toa still image, and may be a moving image. Moreover, it may be configuredso that not only the size of the target but also various presentationmodes can be changed. For example, it is possible to change the color orbrightness (contrast) of the target.

In the above embodiment, the tomographic image and the eyesight valueare stored while being correlated to each other, but the OCT imagecorrelated to the eyesight value is not limited to a tomographic image.For example, a three-dimensional image obtained by three-dimensionalscanning and an eyesight value can also be stored while being correlatedto each other. In this case, it is possible to recognize thethree-dimensional positional relationship between the site of interestin the fundus Ef and the fixation position. Moreover, it is alsopossible to recognize the size (area or volume) of the affected site. Bymaking it possible to acquire such information, the therapeutic effectcan be assessed in more detail than in the case in which two-dimensionaltomographic images are captured.

Moreover, it is also possible to form a tomographic image on anycross-section passing near the eyesight measurement position based onthe volume data obtained by the three-dimensional scanning and storethis tomographic image and the eyesight value while correlating themwith each other. This tomographic image is formed by the image processor230.

In the above embodiment, the OCT measurement is started at the same timeas the start of the eyesight measurement, but the start timing of thesetwo operations may be of any timing. For example, since the eyesightmeasurement takes more time than the OCT measurement, the OCTmeasurement may start in the course of the eyesight measurement.Moreover, it is sufficient if the OCT measurement is executed at leastonce for one scanning region.

When the configuration of above embodiment is utilized, the followingOCT measurement can be performed. In this OCT measurement, the actualfixation position of the eye E is identified by performing scanning withthe signal light LS in two steps.

In the first step, a scanning mode that can be executed for a relativelyshort time is applied, while in the second step, a scanning mode thatcan form a three-dimensional image is applied. It should be noted thatit is possible to reverse the first step and the second step.

As a specific example, the case in which cruciform scanning is appliedin the first step and three-dimensional scanning is applied in thesecond step is described. In the first step, a fixation target is firstpresented to an eye E for fixation. Then, OCT measurement by cruciformscanning is performed on the fundus Ef of the fixed eye E to form atomographic image corresponding to horizontal scanning (horizontaltomographic image) and a tomographic image corresponding to verticalscanning (vertical tomographic image). Here, since cruciform scanning isexecuted instantly, it is believed that there is no deviation of thefixation position of the eye E during the measurement.

Next, as the second step, OCT measurement by three-dimensional scanningis performed on the eye E fixed by the same fixation target as that inthe first step to form a plurality of tomographic images correspondingto a plurality of horizontal scanning (scanning lines). Moreover, theimage processor 230 generates volume data or stack data based on thesetomographic images. Since three-dimensional scanning takes some time (onthe order of a few seconds), the fixation position of the eye E maydeviate during the measurement.

Subsequently, the image processor 230 calculates the image correlationbetween the horizontal tomographic image acquired in the first step andeach tomographic image acquired in the second step, and identifies thecross-sectional position of the tomographic image in the second stepwith the highest correlation value. At this time, the correlation valuebetween various cross-sectional images in the horizontal direction ofthe volume data generated in the second step and the horizontaltomographic image may be calculated and the cross-sectional position inthe horizontal direction of the volume data with the highest correlationvalue may be identified.

Similarly, the image processor 230 calculates the image correlationbetween the vertical tomographic image acquired in the first step andvarious cross-sectional images in the vertical direction of the volumedata acquired in the second step, and identifies the cross-sectionalposition in the vertical direction of the volume data with the highestcorrelation value.

The crossing position of the horizontal cross-sectional position and thevertical cross-sectional position in the three-dimensional image asidentified above is the fixation position of the eye E. Consequently,the fixation position of the eye E on the three-dimensional imageacquired in the second step can be easily identified. Furthermore,three-dimensional morphology of the fundus Ef near this fixationposition can be recognized, allowing the recognized information topossibly aid in diagnosis and treatment.

A modification example in which the OCT measurement is performed basedon the eyesight measurement results is described. In this modificationexample, a visual target for measuring eyesight corresponding to apredetermined eyesight value is projected on the fundus Ef. This processis performed by the controller 210. This predetermined eyesight value isa preliminarily set eyesight value such as an eyesight value consideredas having good eyesight (for example, 1.0). The subject inputs theresponse content against this visual target for measuring eyesight usingthe input device 300.

The controller 210 determines whether the input response content is trueor false. This process is executed by, for example, judging whether ornot the direction indicated by the input device 300 matches thedirection of the rift in the Landolt ring displayed on the LCD 39 as avisual target for measuring eyesight, and determining it as a correctanswer if they match or determining it as a wrong answer if they do notmatch.

If the response content is determined as a correct answer, thecontroller 210 controls the scan drive 70 to change the direction of theGalvano mirrors 43, 44 and scans the scanning region superposed on theprojection region of said visual target for measuring eyesight on thefundus Ef with the signal light LS.

The CCD image sensor 120 detects interference light LC of the signallight LS and the reference light LR. The image forming part 220 forms atomographic image of the above-mentioned scanning region based on thedetection results. When this scanning region is a two-dimensionalregion, the image forming part 220 forms a tomographic image on each ofa plurality of cross sections (scanning lines) within this scanningregion, and the image processor 230 forms a three-dimensional image ofthis scanning region based on these tomographic images. The maincontroller 211 stores the formed OCT image (tomographic image orthree-dimensional image) and above-mentioned predetermined eyesightvalue in the storage 212 while correlating them to each other. At thistime, information indicating the projection region of the visual targetfor measuring eyesight on the fundus Ef (for example, display positionof the visual target for measuring eyesight on the LCD 39, position ofthe projection region on the fundus image, etc.) may be stored whilebeing correlated with the OCT image and the predetermined eyesightvalue.

According to such a modification example, an OCT image of a site in thefundus Ef having at least the predetermined eyesight value can beautomatically acquired.

As a further modification example, it is also possible to configure suchthat the OCT image of the measurement site can be acquired even when theeyesight value of the measurement site in the fundus Ef is below thepredetermined value. As a specific example, if the response to thevisual target for measuring eyesight of a predetermined eyesight value(for example, 1.0) is determined to be wrong, the controller 210 allowsthe visual target for measuring eyesight corresponding to the next lowereyesight value (for example, 0.8) to be displayed on the LCD 39. Then,if a correct answer is obtained for this visual target for measuringeyesight projected on the fundus Ef, the controller 210 controls thescan drive 70 to change the direction of the Galvano mirrors 43, 44 andscan the scanning region superposed on the projection region of thisvisual target for measuring eyesight on the fundus Ef with the signallight LS. The image forming part 220 etc. forms an OCT image based onthe detection results of interference light LC of the signal light LSand the reference light LR. The main controller 211 stores the formedOCT image and above-mentioned eyesight value in storage 212 whilecorrelating them to each other. At this time, information indicating theprojection region of the visual target for measuring eyesight on thefundus Ef may be stored while being correlated to the OCT image and theeyesight value.

It should be noted that, if a wrong answer is obtained again, the visualtarget for measuring eyesight corresponding to still lower eyesightvalues may be used to conduct the examination. Moreover, it is alsopossible to preset the lowest eyesight value for conducting the eyesightmeasurement.

In the above embodiment, the position of the reference mirror 114 ischanged so as to change an optical path length difference between theoptical path of the signal light LS and the optical path of thereference light LR. However, a method for changing the optical pathlength difference is not limited thereto. For example, it is possible tochange the optical path length difference by moving the retinal cameraunit 2 and the OCT unit 100 with respect to the eye E to change theoptical path length of the signal light LS. Moreover, in a case that anobject is not a living site or the like, it is also effective to changethe optical path length difference by moving the object in the depthdirection (z-direction).

The computer program used in the above embodiments can be stored in anykind of recording medium that can be read by a drive device of acomputer. As this recording medium, for example, an optical disk, amagneto-optic disk (CD-ROM, DVD-RAM, DVD-ROM, MO, and so on), and amagnetic storage (a hard disk, a floppy Disk™, ZIP, and so on) can beused. Moreover, it is possible to store into a storing device such as ahard disk drive and a memory. Besides, it is possible totransmit/receive this program through a network such as internet or LANetc.

What is claimed is:
 1. A fundus observation apparatus comprising: aprojection part that projects visual target for measuring visiondisplayed on a display part to the fundus of an eye; an optical systemthat splits light outputted from a light source into signal light andreference light, generates interference light by superposing said signallight that has passed through said fundus and said reference light thathas passed through a reference optical path, and detects saidinterference light; a scanning part that scans said fundus with saidsignal light; a controlling part that controls the scanning region ofsaid signal light scanned by said scanning part each other; an imageforming part that forms an image of said fundus based on the detectionresults of interference light generated by superposing said signal lightwith which said scanning region is scanned and said reference light; andan operation part for inputting response contents for said visual targetfor measuring vision projected to said fundus; and a vision measurementpart that examines vision of the eye based on the response contents. 2.The fundus observation apparatus according to claim 1, wherein: saiddisplay part displays a fixation target for fixing said eye.
 3. Thefundus observation apparatus according to claim 2, wherein: saidcontrolling part begins the measurement in the scanning region at thesame time as the start of the eyesight measurement.
 4. The fundusobservation apparatus according to claim 1, wherein: said controllingpart controls so as to overlap the projection region of said visualtarget for measuring vision projected by said projection part and thescanning region of said signal light scanned by said scanning part eachother.
 5. The fundus observation apparatus according to claim 4, furthercomprising a storage part that stores said formed image and a visionvalue measured using said visual target for measuring vision whilecorrelating them with each other.
 6. The fundus observation apparatusaccording to claim 1, wherein: said controlling part controls saidprojection part based on the scanning region of said signal lightscanned by said scanning part to overlap the projection region of saidvisual target for measuring vision in said fundus on the scanning regionof said signal light.
 7. The fundus observation apparatus according toclaim 6, wherein: said display part displays a fixation target forfixing said eye along with said visual target for measuring vision; saidprojection part projects said displayed fixation target on said fundusalong with said visual target for measuring vision; and said controllingpart changes said projection region by changing, based on said scanningregion, the relative display positions of said visual target formeasuring vision and said fixation target displayed by said displaypart.
 8. The fundus observation apparatus according to claim 1, wherein:said controlling part controls said scanning part based on the displayposition of said visual target for measuring vision displayed by saiddisplay part to overlap the scanning region of said signal light in saidfundus on the projection region of said visual target for measuringvision.
 9. The fundus observation apparatus according to claim 1,wherein: said controlling part allows said visual target for measuringvision corresponding to different vision values to be projected on saidfundus, by allowing said visual target for measuring vision of differentsizes to be displayed on said display part to change the size of saidprojection region.
 10. The fundus observation apparatus according toclaim 9, wherein: said projection part projects said displayed visualtarget for measuring vision to the fundus of an eye via a predeterminedoptical path, said optical system conducts said signal light via apredetermined optical path, said predetermined optical path is providedwith a focusing lens that moves along an optical axis thereof to changethe focus position of light towards said fundus; and said controllingpart adjusts the size of said visual target for measuring visiondisplayed on said display part based on the position of said focusinglens.
 11. The fundus observation apparatus according to claims 9 or 10,wherein: said controlling part changes the size of said visual targetfor measuring vision displayed on said display part based on said inputresponse contents, and determines the vision value of said eye based onsaid response contents according to this change.
 12. The fundusobservation apparatus according to claim 1, wherein: said controllingpart controls said projection part to project said visual target formeasuring vision corresponding to a predetermined vision value to saidfundus, determines whether said input response contents for this visualtarget for measuring vision are true or false, and if it is determinedthat they are correct, then controls said scanning part to scan saidscanning region overlapping the projection region with said signallight.
 13. The fundus observation apparatus according to claim 1,wherein: said light source outputs invisible light as said low-coherencelight.
 14. The fundus observation apparatus according to claim 13,wherein: said light source outputs near-infrared light of centerwavelength within the range substantially from 1050 to 1060 nm.